The present invention relates to a power transmission mechanism such as that employed in a compressor to connect and disconnect the compressor to a power source.
Japanese Unexamined Patent Publication No. 8-121336 describes a typical power transmission mechanism for a compressor. As shown in FIG. 7, the compressor has a housing 102. An angular bearing 103 is fitted on the housing 102 to rotatably support a pulley 101 by way of a sleeve 105. A belt 104 connects the pulley 101 to a power source. The pulley 101 is connected to a drive shaft 108 by a rubber ring 107 and a coupling disk 106. The rubber ring 107 is adhered to the pulley 101 and to the coupling disk 106. The coupling disk 106 has a center bore 106a through which the drive shaft 108 is inserted. A nut 108a fastens one end of the drive shaft 108 to the coupling disk 106. A torsion spring 109 is arranged on the drive shaft 108. The spring 109 torsionally grips the drive shaft 108. The spring 109 has an end 110 that is received in an engaging recess 111 defined in the coupling disk 106.
The power source produces rotation that is constantly transmitted to the drive shaft 108 by way of the belt 104, the pulley 101, the sleeve 105, the rubber ring 107, the coupling disk 106, and the torsion spring 109. When the load applied to the drive shaft 108 becomes excessive, the spring 109 is twisted and deformed. This enlarges the diameter of the spring 109 and thus decreases the tightening force of the spring 109 with respect to the drive shaft 108. As a result, slippage occurs between the spring 109 and the drive shaft 108. Accordingly, the transmission of power from the power source to the drive shaft 108 is stopped when the load becomes excessive.
The rotation of the coupling disk 106 is transmitted to the spring end 110. The torsion spring 109 then transmits the rotation to the drive shaft 108. Therefore, the transmission of power from the pulley 101 to the drive shaft 108 pulls the spring end 110 and produces a bending force that is applied to the drive shaft 108. The bending force may result in radial loads acting on bearings and seals. This can lead to biased wear of these parts and may thus cause unstable rotation of the drive shaft 108 or degrade the sealing property of the seals.
To prevent a bending force from acting on the drive shaft 108 when the end of the torsion spring 110 is pulled, the spring end 110 and the engaging recess 111 must be formed with precision so as to restrict the movement of the spring end 110. However, this increases the production costs.